Electrographic imaging processes and techniques have been extensively described in patents and other literature. These processes may take the form of electrophotographic techniques whereby a photoconductive insulating material is first electrostatically charged and then imagewise exposed with light to form a latent image. Exemplary electrophotographic imaging processes are disclosed in U.S. Pat. Nos. 2,221,776; 2,277,013; 2,297,691; 2,357,809; 2,551,582; 2,825,814; 2,833,648; 3,220,324; 3,220,831; 3,220,833 and many others.
Generally, these processes have in common the steps of forming a latent electrostatic charge image on an insulating electrographic element. The electrostatic latent image is then rendered visible by treatment with an electrostatic developing composition or developer.
Conventional developers include a carrier that can be either a triboelectrically chargeable, magnetic material such as iron filings, powdered iron or iron oxide, or a triboelectrically chargeable, non-magnetic salt such as sodium or potassium chloride. In addition to the carrier, electrostatic developers include a toner which is electrostatically attractable to the carrier. Useful toners include powdered pigment resins made from various thermoplastic and thermoset remains such as polyacrylates, polystyrene, poly(styrene-coacrylate), polyesters, phenolics and the like, and can contain colorants such as carbon black or organic pigments or dyes. Other additives such as charge control agents and surfactants can also be included in the toner formulation.
Other examples of suitable toner compositions include: the polyester toner compositions of U.S. Pat. No. 4,140,644, the polyester toners having a p-hydroxybenzoic acid recurring unit of U.S. Pat. No. 4,446,302, the toners containing branched polyesters of U.S. Pat. No. 4,217,440, and the crosslinked styrene-acrylic toners and polyester toners of U.S. Pat. No. Re. 31,072, the phosphonium charge agents of U.S. Pat. No. 4,496,643, and the ammonium charge agents of U.S. Pat. Nos. 4,394,430, 4,323,634, and 3,893,935. These toners can be used with plural component developers with the various carriers such as the magnetic carrier particles of U.S. Pat. No. 4,546,060 and the passivated carrier particles of U.S. Pat. No. 4,310,611.
Toner binder compositions can be manufactured by various methods. For example, conventional condensation polymerization, such as disclosed in U.S. Pat. No. 4,140,644 to Sandhu, et al., U.S. Pat. No. 4,217,440 to Barkey, and U.S. Pat. No. Re. 31,072 to Jadwin, et al, is often utilized. Toners can also be manufactured by a form of suspension polymerization known as "limited coalescence". Exemplary limited coalescence techniques are described, for example, in U.S. Pat. No. 4,833,060 to Nair, et al., U.S. Pat. No. 4,835,084 to Nair, et al., and U.S. Pat. No. 4,965,131 to Nair, et al.
It is known that, depending on the type and nature of the resin(s) used, the resulting toner will exhibit varying physical properties. For example, the branched polyester toners disclosed in U.S. Pat. No. 4,217,440 exhibit such favorable properties as high glossability, good flow properties during fusing, easy dispersibility of pigment, higher grindability, and superior charging rates as positive toners. In addition, dyes are generally more soluble in branched polyesters and it is generally easier to disperse pigment in branched polyesters. Toners derived from the polymerization of vinyl monomers exhibit superior fuser reliability in that the toner particles do not accumulate or stick to the fusing roll as readily as typical polyester toner particles.
Because the favorable properties exhibited (or not) by a toner are often a product of the toner binder's structure, there are few toner compositions that exhibit the properties of, for example, both a polyester and a polyvinyl toner. Therefore, there continues to be a need for toners exhibiting the various favorable properties outlined above that can be practicably made by known methods of toner manufacture.